Modern RF devices, such as mixers, upconverters, downconverters, power amplifiers and the latest highly integrated multifunction ICs, often require operation mode tuning using multiple independent voltage references (VREF). In some circumstances, the reference voltages need to be re-adjusted at runtime for various operation environments such as temperature, frequency, power level, etc. Such devices are usually calibrated during product manufacturing, for example, individually calibrated for each manufactured unit, and the values of the reference voltages are stored inside the on-board electrically erasable programmable read-only memory (EEPROM).
A most common approach to provide multiple reference voltages to the controlled device is illustrated in FIG. 1, where a digital-to-analog converter (DAC) with multiple channels is used.
In a modular design approach, a CPU/MPU with a DAC are disposed on one board referred as the “control board”, while the controlled device, such as mixers, upconverters, etc., are disposed on a different board referred as the “controlled board”. The physical interface between the control board and the controlled board is predefined so that the same type of the control board can be connected to different predefined types of the controlled board. FIG. 2 depicts a structure of a revised system to provide reference voltage to a mixer on a controlled board.
However, a connector of the control board has a limited and fixed number of analog lines determined by the original design of the controlled board. Future revisions or new types of the controlled board may require more reference voltages than originally designed. Therefore, the interface of a current controlled board may not be able to provide enough analog lines to meet the new design requirements. FIG. 3 depicts a compatibility problem of the revised system to provide reference voltage to a mixer on a controlled board. Note that the mixer needs two reference voltage signals but the control board can only provide one.